The present invention relates to data communications systems, and more particularly, to a data processing apparatus comprising nodes provided to the data processing apparatus or to a peripheral apparatus and disposed at a plural number of points which are mutually separated by a certain distance, and optical transmission cables connecting those control apparatus, and provided with a fiber distributed data exchange interface (hereinafter termed an FDDI) that can be used for optical local area networks to transmit/receive, at either high speed or low speed, various types of data between the processing apparatus and/or control apparatus, and the peripheral apparatus.
In recent years, local area networks (hereinafter, termed LAN) have been used at an increasing rate in many different fields. Amongst these fields, one that is attracting much attention in the field of next generation, high-speed and wide-area LAN are fiber distributed data exchange interfaces for which standardization has been defined by the American National Standards Institute (hereinafter, termed ANSI-FDDI). These ANSI-FDDI use optical fiber as the transmission path and are 100 Mbps ring-shaped LAN that use the token passing method as the transmission control method. Although the ANSI has practically completed the standardization of the FDDI ratings, FDDI are being studied in the fields of the computers and communications industry since large-scale integrated circuits (hereinafter, termed LSI) and protocol processing software in conformity with the FDDI ratings have come to be available from semiconductor manufacturers.
For example, one proposal for the use of FDDI is to configure a packet exchange network so that data can be both sent and received at high speeds between multiple mainframe computers, between mass storage systems connected to mainframe computers, or connected between mainframe computers and other peripheral equipment. Furthermore, these FDDI are thought to be capable of being used as backbone networks connecting between LAN systems such as the Ethernet and MAP (manufacturing automation protocol) systems and the like.
MAP is a communications protocol for the automization of factories and is the practical standard for LAN for factory automation purposes (known as FA-LAN). LAN using FDDI having a plural number of nodes mutually connected in a ring shape generally have various functions, such as transmission path control functions, that can stop transmission requests from each node, in accordance with the transmission region that can be used by the network and acquire transmission path usage rights, transmission and receive function for the data from each node, transmission system obstruction detection functions, obstruction portion separation functions, and transmission system reconfiguration functions, etc.
As has been described above, in token-passing LAN used for LAN having FDDI, transmission rights known as tokens are successively received between each of the nodes in the system to prevent a plural number of nodes from sending at the same time. These systems are configured so that data can be sent within a predetermined set time, by those nodes that have received tokens. Accordingly, it is possible to have definitive transmission path access and so this token passing method is used in MAP systems that require realtime control.
MAP systems are one typical use of the token passing method and these systems have arranged on a factory floor for example, a computer (C), a programmable controller (PC), robots, computerized numerical control process machines (CNC) and other types of intelligent equipment configured into a network so that it is possible to achieve factory automation (FA) through the exchange between these items of equipment, of various types of data such as production management information, maintenance management information, control information, manufacturing performance information and the like. However, along with the further development of networks of intelligent equipment, factory automation has come to be unified with continuous process automation (PA) that has its own, different characteristics, to therefore give rise to the need to develop unified control systems operating under a single control LAN, and that are applicable to entire factories. These PA systems network the computers that monitor the manufacturing and that manage production, the programmable controllers (PC) that perform continuous and high-speed control of mainly equipment, and digital instrument control systems (DCS) that control instruments, etc., so that the unification of the control processes is promoted by enabling distributed control.
However, in such unified control systems including the PA systems described above, there is the problem that it is required to have realtime data exchange which is far more accurate when compared to that which is possible by FA systems alone. The reason for this is that in the case of continuous process control, the data that should be sent must be controlled so that there is a responsiveness in the order of several milliseconds. (In the case of factory automation alone, the response time of the data transmission functions required of the programmable controllers (PC) described above, is sufficient if it is in the range of several hundreds of milliseconds to several seconds.)
Furthermore, in control systems that are unified with PA, amongst the data that is exchanged between equipment is not only data which has an extremely high degree of urgency necessary for each PC control cycle of the programmable controllers and which is in units of several milliseconds, but also data for the previously described DCS operation and data for alarm and monitoring which are in units of several hundreds of milliseconds, instrument data and data for program downloading which is given background processing, or data for production management, maintenance management and manufacturing performance and the like, all of which have a relatively low degree of urgency. In such unified control systems as described above, it is required to have a network that can give a high priority to the transmission of data that has a high degree of urgency and at the same time perform the definite transmission of data that has a low degree of urgency.
In this manner, the data that is passed between the computers, programmable controllers (PC), digital instrument control systems (DCS) and other equipment connected in process control system LAN, is that which is generated in accordance with sudden transmission requests, and that which is always generated periodically in accordance with its degree of urgency as described above. Accordingly, it is therefore necessary for each node to have cyclic transmission control within a certain time period in accordance with the degree of urgency for the data of each level, and each of the items of equipment must be able to receive and renew the contents of the data for each of the received cycles. It is also necessary that the data be sent and output to the LAN so that it has priority over data with lower levels of priority (i.e. less urgency).